Vacuum apparatus

ABSTRACT

VACUUM APPARATUS WITH A CHAMBER AND DIFFUSION PUMP FOR EVACUATING THE CHAMBER VIA A HIGH CONDUCTANCE QUONSET-HUT FORM EXTENSION OF THE CHAMBER. THE EXTENSION IS A SEMI-CYLINDRICAL SHELL WITH A THICK FLAT PLATE AS A BASE. THE DIFFUSION PUMP INLET IS CONNECTED TO A PORT IN THE FFLAT PLATE BASE VIA A DEMOUNTABLE SEAL AND HAS AN EXTRA SEALING PROVISION FOR ALLOWING A VALVE WITHIN THE EXTENSION TO SEAT ON THE DIFFUSION PUMP INLET. THE ARRANGEMENT AFFORDS OVER-ALL HIGH SPEED AND THROUGHPUT CONSISTENT WITH STRUCTURAL INTEGRITY AND ECONOMY OF MANUFACTURE.

Jan. 5, 1971 I BASSAN 3,552,885

VACUUM APPARATUS Filed Sept. 19, 1968 T T i/zez J INVENTOR.

I I 5mm M/IV 54.55/24 F l G. 2

United States Patent 3,552,885 VACUUM APPARATUS Benjamin Bassan, Framingham, Mass., assignor to Norton Company, Worcester, Mass., a corporation of Massachusetts Filed Sept. 19, 1968, Ser. No. 760,960 Int. Cl. F04f 9/00 U.S. Cl. 417-452 3 Claims ABSTRACT OF THE DISCLOSURE Vacuum apparatus with a chamber and diffusion pump for evacuating the chamber via a high conductance Quonset-hut form extension'of the chamber. The extension is a semi-cylindrical shell with a thick flat plate as a base. The diffusion pump inlet is connected to a port in the fiat plate base via a demountable seal and has an extra sealing provision for allowing a valve Within the extension to seat on the diffusion pump inlet. The arrangement affords over-all high speed and throughput consistent with structural integrity and economy of manufacture.

The present invention realtes to vacuum apparatus particularly to large vacuum chambers on the order of 100 cubic feet and larger with vacuum pumping systems including a diffusion pump with rated speed of 10,000 liters per second and more. Such systems are used as industrial coaters and furnaces and as outer space simulating environmental test equipment.

The particular requirements of such system include a high conductance connection from the chamber to the diffusion pump inlet consistent with structural integrity of the connection against the pressure differential across its walls and insertion of a valve between chamber and pump and accommodating tall vertically arranged vacuum pumps without digging a pump pit.

The conventional approach is a tubular manifold ex tending from the chamber to a tubular body valve which is connected at its outlet end to a diffusion pump inlet. This involves high conductance loss and expense. Another approach in the art with higher conductance involves a rectangular cross section extension of the chamber with a valve seat on a bottom plate of the extension and a valve disc in the extension. Internal reinforcing members prevent collapse of the structure when vacuum is drawn inside; these members negate some of the inherent improvements in conductance of the structure and add to expense of construction.

It is an object of the present invention to provide an improvement in such apparatus affording a higher degree of conductance consistent with structural integrity and economy.

It is a further object of the invention to provide a vacuum apparatus which provides maximum head-room for accommodating a tall vertically arranged pump consistent with the foregoing object without digging a pump pit.

The invention generally comprises an improved vacuum apparatus comprising a large size chamber (at least 100 cubic feet volume) evacuated by a pumping system comprising a high speed diffusion pump (20,000 liters per second or more rated speed) via a Quonset-hut form (semi-cylindrical) extension of the chamber. The extension has a thick flat plate as a base and a pumping port in the plate larger than the diffusion pump inlet. The diffusion pump is demountably coupled to the plate and has an inlet flange sealed around the port periphery. There is a valve disc carried in the extension which is movable between a retracted position where it allows a conductance area at least equal to the pump inlet area and a closed position where it is seated. The valve seats 3,552,885 Patented Jan. 5, 1971 on a portion of the pump inlet flange which extends inwardly of the periphery of the exit port. Thus there is no need to machine a valve seat by reaching through the extension itself and the semi-cylindrical form is made feasible. This avoids the need for conductance limiting internal reinforcements.

Other objects, features and advantages of the invention will in part be obvious and will in part appear hereinafter.

The invention is now described specifically with reference to the accompanying drawings wherein FIG. 1 is a side view of the improved apparatus and FIG. 2 is an expanded cross section view of the extension cut and viewed as indicated by line II-II in FIG. 1.

Referring now to FIG. 1, the apparatus comprises a vacuum chamber 10 of cylindrical form with spherical dished heads 12. A front one of said heads is flanged to form a door and the other head is welded to the cylinder and accommodates the pump-out extension described below. The apparatus is supported from the floor with posts 14 and saddles 15 as necessary.

The chamber is of the conventional vacuum tight construction. Connected to the chamber is a conventional vacuum pumping system comprising a diffusion pump 16, booster pump 18 and forepump 20. Pumping cycle is controlled by a roughing valve 22, a foreline valve 24, a high vacuum valve 26 and air release valve 28.

Leading from the rear of the chamber 10 is a Quonsethut form extension 30 which includes a part-cylindrical (e.g. semi-cylindrical) concave Wall 32 with a dished head 34 of part spherical form forming the rear of the inwardly smoothly concave extension and a thick flat plate 36 completing the enclosure of the extension. The spherical radius of 34 is twice the cylindrical radius of 32.

The flat plate 36 includes an exit port 37 essentially coinciding with an inlet port 17 of the diffusion pump.

Referring now to FIG. 2, the cooperating extension high vacuum valve and pump structure is shown in greater detail. The wall 32 is steel of a thickness of A to inch. These thin sections are tolerable in view of the in herent rigidity of cylindrical design. No internal reinforcing ribs or plates are required, although one or more external ribs are advantageously applied to the semi-cylindrical wall. The plate 36 has a thickness of 1 to 1 /2 inches, preferably 1%, to withstand the atmosphere to high vacuum pressure differential across it without buckling. Parts 32, 34, 36 are welded together in accordance with conventional welding practice for vacuum apparatus.

The pump 16 has a flange 161 at its inlet which is demountably coupled to the outside of plate 36, plate 36 being machined in the region of coupling to a 63-RMS finish at the sacrifice of a inch loss of thickness in that region. The demountable seal is made essentially vacuum tight by an O-ring gasket 162 which may be mounted in a groove provided in either the pump flange or extension plate for that purpose (the other of the two members being suitably machined).

The valve comprises a valving member-disc 261 driven via actuating shaft 262 by servomotor 263. The shaft is supported by a bronze bushing 264 and sealed by an O- ring 265. The bushing passes through the semi-cylindrical Wall 32 and is supported from the wall by a collar 266 which is of substantially smaller area than the opposing exit port 37.

The valving member seats on an inwardly extending (with respect to exit port 37) portion of flange 161 and is sealed by a gasket 163 which may be mounted on the valving member or flange (the other of the two members being suitably machined to 63 r.m.s. finish).

The valving member 261 is movable between the sealing position shown in solid lines in FIG. 2 and the retracted position shown in dashed lines in FIG. 2. The annular passage area cleared by the valving member disc 261 in its retracted position should be at least equal to and preferably greater than the inlet opening area of the pump 16. To this end, the length of valve movement L of the disc should be equal to or greater than the diameter (D) of opening 17 of pump 16 divided by 4.

The valving member is flexibly connected to its actuating shaft so that it finds its own level on flange 261 for proper seating and good vacuum sealing.

Several possible variations can be made in the above described invention. For instance the diffusion pumps could be replaced by other equivalent vapor vacuum pumps which produce high vacuum levels (1 X mm. Hg or less) at high speeds (10,000 liters per second or more). The vapor vacuum pump may not necessarily require vertical arrangement in which case the pump cou d be horizontal and plate 36 vertical. The extension 30 may lead directly from chamber 10 as in FIGS. 1-2 or be connected to the chamber via a cylindrical pipe. The latter alternative would be useful for accommodating a very tal vertical diffusion pump with the extension above the pump and the tubular connection going up from a low chamber to meet the extension. It will also be understood that the inlet of the vapor vacuum pump for purposes of the present specification includes the inlet of pump accessories such as bafiie, cold trap or spool piece vacuum pump inlet flange can include the inlet flange of such accessory or an adapter flange of such accessory or an adapter flange in such cases. It is also possible to provide baffle or creep barrier or cold trapping structure in the portion of the extension not occupied by movement of the valving membe. For instance a creep barrier in the form of a A by inch cross section metal strip can be placed around the interior of the extension between the chamber and high vacuum valve.

Still other alternatives within the scope of the invention Will be apparent to those skilled in the art once given the benefit of the present disclosure. Accordingly it is intended that the foregoing disclosure shall not be considered in a limiting sense except as stated in the claims.

What is claimed is:

1. An improved vacuum apparatus combination comprising (a) a vacuum chamber,

(b) a pumping system including a diffusion pump with an inlet port surrounded by an inlet flange connected 4 to said chamber for producing and maintaining low pressures of the high vacuum region in the chamber,

(c) means forming an extension of said chamber with a wall in the form of part cylindrical cross section with a flat plate base of greater thickness than the thickness of the part-cylinder wall, the said wall and plate assembly being constructed to withstand the differential of external atmospheric pressure versus internal high vacuum and (d) an exit port in the said plate for connection to the inlet of the diffusion pump, said plate and pump inlet flange being constructed and arranged for forming a demountable seal on the outside of the plate around the periphery of the exit port, the said in et flange also extending inwardly of said exit port.

2. The apparatus of claim 1 further comprising (e) a valving member located within said extension and said member and pump flange being constructed and arranged so that the valving member seats on a portion of the pump flange extending inwardly of the extension port, and

(f) means for moving the valving member between said seated position and a retracted position wherein the clearance area between the valving member and extension walls is no less than the pump inlet area.

3. The apparatus of claim 2 wherein said moving means (f) comprises a shaft passing through the said semi-cylindrical wall of the extension and the apparatus further comprising a bearing seal mounted on said wall and support- 30 ing the shaft while sealing it against in-leakage of air.

References Cited UNITED STATES PATENTS 2,806,644 9/1957 Warren 230101 3,141,606 7/1964 Landfors 230101 3,297,872 1/1967 Kennedy 230-101X 3,319,876 5/1967 Hunter 230-101 3,310,227 3/1967 Milleron 230101 3,446,422 5/ 1969 Bailleul-Langlais et al. 23035 DONLEY J. STOCKING, Primary Examiner W. I. KRAUSS, Assistant Examiner U.S. Cl. X.R. 417- 

